This invention relates to printers having a positionally adjustable printhead and, more particularly, to an adjustable printhead-carrying yoke for a printer which permits dynamic adjusting of the printhead's fore and aft and skew positions comprising, a fixed yoke portion carried by the printer; a movable yoke portion carrying the printhead; fore and aft adjusting means for moving the movable yoke portion thereby adjusting the printhead's fore and aft position while the printhead is printing; and, skew adjusting means for moving the movable yoke portion thereby adjusting the printhead's skew while the printhead is printing.
Many printers for printing on a media employ a printhead positioned over a supporting platen plate or platen roller. Depending on the size of the printer and the mode of printing (e.g., impact, thermal activation, thermal transfer), the alignment of the printhead over the platen can be quite critical. Particularly in small label printers employing a thermal transfer printing process such as those manufactured by the assignee of this application, a small change in printhead alignment can make the difference between acceptable and unacceptable print quality.
Printhead alignment is typically a manufacturing and assembly process that remains constant once it is achieved barring some outside force that misaligns the printhead. Since it is critical, it is not something that the manufacture wants the end user to re-adjust. If re-adjustment is required, it is best accomplished by a trained repair person. Also, since it is critical, if the adjustment process is not quick, easy, and repeatable, it can add significantly to manufacturing time and cost as well as cause a bottleneck in the throughput of the manufacturing process.
In the prior art, printhead alignment is a static process. The adjustment process is depicted in FIG. 1 and 2. The printhead 10 is carried by a shaft 12 mounted to the bottom piece 14 of a yoke assembly 16. The top piece 18 of the yoke assembly 16 is mounted on a shaft 20 for lateral adjustment. Lateral adjustment is not a problem, so that will not be addressed further. The top piece 18 and the bottom piece 14 are joined by a pair of machine screws 22 passing through oversized bores 24 in the top piece 18 and threaded into the bottom piece 14. The top piece 18 is held in place by the shaft 20. Thus, with the machine screws 22 loosened, the bottom piece 14 can be moved forward and backward and skewed is depicted in FIG. 2 within the limits of the clearance fit of the machine screws 22 within the bores 24.
To adjust the printhead 10 using the yoke assembly 16, an adjusting fixture (not shown) is attached to the printhead 10 and the machine screws 22 are loosened. The fixture is then positioned on the platen (not shown). The machine screws 22 are then tightened and the fixture removed. The printer is then reassembled and tested for print quality. If not acceptable, the process is repeated. The same thing is true if a repair person has to re-align the printhead 10 in the field.
As can be appreciated, since the static alignment process is not exact and not repeatable, sometimes it provides acceptable print quality the first time it is done and sometimes it doesn't. And, there is no comparison since it is a static process. That is, the adjuster can not compare one position of alignment to another to determine the best position for the particular printer. This is a result of so-called "tolerance build-up". As is common in all manufacturing processes, each part in a printer is built to tolerance. If it is to be an inch long, that means that it can be an inch plus or minus the tolerance allowed. In general, tolerances average out and are not critical. In the area of printhead alignment, however, they are critical and if a particular printer as assembled has all its tolerances on one side (i.e. all plus or all minus), the build-up of the sizing errors can produce a problem for printhead alignment using the fixture, which is designed for a low tolerance or ideal printer.
Wherefore, it is an object of the present invention to provide a method and apparatus for dynamically adjusting printheads in printers.
It is another object of the present invention to provide a method and apparatus for adjusting printheads in printers which is not subject to tolerance build-up problems.
It is still another object of the present invention to provide a method and apparatus for adjusting printheads in printers which allows the adjuster to compare the print quality of different positional alignments.
Other objects and benefits of this invention will become apparent from the description which follows hereinafter when read in conjunction with the drawing Figures which accompany it.